The present invention is related to the general surgical repair of separated body tissues, and more particularly to internally fixating and stabilizing such body tissues, specifically bones.
In the present state of the art, there are a number of systems available to repair biological tissues separated in surgery or by injury. These products serve to approximate and stabilize the tissues so that healing may commence and provide compression in the interface to promote anatomical heal of tissue. With the correct amount of compression applied to the interface of the tissue portions to be joined, signals are sent to the tissue, thus allowing the tissue to remodel in proper anatomical position. The amount of compression applied to the tissue interface needs to be appropriate to the type of tissue that is being healed.
Twisted wires are typically used to keep bone fragments together so they may heal. Twisted wires only hold tension as long as the twisted wire pair remains stable. Often the wires untwist too soon, thus failing to keep the bone fragments together so that they may heal. Wires can also cut into bone fragments, allowing them to separate so that healing is difficult.
When it is necessary to access the thoracic cavity for a medical procedure, for example, it is required to cut the sternum into two pieces using a sternal saw. Once the procedure is completed within the thoracic cavity, the sternum must be repaired. For such repairs, it is known to use a dynamic compression device. Some of the drawbacks of this typical device, and others which are used include the fact that bulky spring materials used in such devices, while occupying substantial space, often do not store much energy. Some use polymer elastic bands, while others use coiled springs. Additionally, wires are sometimes used to wrap the bones into position in compression with one another. However, wires can have sharp ends that can damage adjunctive tissues. Knot stacks in suture can interfere with the natural movement of surrounding tissues. Another disadvantage of these prior art dynamic compression devices is that current banding systems that incorporate a biasing mechanism to achieve dynamic compression put the biasing mechanism in line with the band or suture. This practice competes with precious space at the healing site. Bands of suture are used to approximate tissues so that they may heal. It is desirable to obtain the best purchase possible on the tissue, so that the binding mechanics offered by the suture may be utilized. The best purchase is optimized by ensuring that the suture has the greatest contact area with the tissue. If a biasing mechanism is interfering with this concept, the biasing mechanism may diminish the suture's ability to hold the tissues together.
In addition, the current banding systems have stiff bands that are not compliant with bony undulations. Flat sutures are used, but are tedious to tie and do not hold reliably.
The banding systems of the present invention are therefore attractive for use in sternal closure because they offer some distinct advantage over twisted wires commonly used in the procedure.
Bands address the issues wires have, as noted in the following discussion. A band, by definition, is wide. In being wide, a band distributes its forces over a wider surface area. This inhibits the band from digging into the bone. In being wide, a band also affords a larger cross-sectional area, whereby more material may be realized, thus presenting the opportunity to offer as much strength in the construct as is necessary to hold the bone fragments together. As such, bands address two main weaknesses of twisted wires. These weaknesses are: digging into the bone fragments being held together, and not having sufficient cross sectional area.
However, with respect to bands, their strength is accompanied by stiffness, as mentioned elsewhere herein. The larger cross-section of the band significantly increases the stiffness of the band. While stiffness and rigidity are good attributes in the sense that they can stabilize the bone union, these attributes can also prevent the band from following the contours of the bone when inserted. This can lead to capturing tissues underneath the band that ultimately destabilize the union as the tissues continue and disappear over time.
Binding the band ends together can also impose some problems. Generally this binding involves a mechanism on the band end that interfaces with holes or slots or contours on the other band end. This creates a tensioning system that is incremental in nature. As in the twisted wire systems, this mechanical interface of the two ends id the weakest link in the banding system. This mechanical interface becomes conductive to fine tuning the tension, so this is problematic. Flat sutures have been used to tie tissues together, but the residual tension supplied in such a knotted structure is insufficient for optimum healing. There is a lot of fuss and time associated with trying to keep and hold a desirable tension with these sutures. What is needed is an attachment means that provides variable tensioning.
Another problem associated with banding systems is that their tension holding capabilities are not sufficient for the environment in which they operate. Tension holding ability can be increased or enhanced by increasing friction at the binding interface of the band. What is needed however is a banding system with the ability to hold tension by selectively increasing friction at the binding interface during locking and/or after locking without increasing friction while tensioning.
What is needed, therefore, are improved devices and techniques for holding two tissue portions in a state of compression and tension that address and overcome these shortcomings in an innovative way.